Stable lead alkyl compositions and a method for preparing the same



United States Patent 3,133,105 STABLE LEAD ALKYL COUSITIONS AND A METHGD FUR PREPARING THE SAME Albert P. G raitis, Hymin Shapiro, and James D. Johnston, Baton Rouge, La, assignors to Ethyl Corporation,

New York, N.Y., a corporation of Virginia No Drawing. Filed June 8, 1962, Ser. No. 2%,972

5 Claims. Cl. 260-437) This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates to methods for inhibiting the thermal decomposition of 'alkyllead compounds when subjected to temperatures above 100 C., at which temperature thermal decomposition becomes appreciable.

Generally this invention contemplates inhibiting the thermal decomposition of alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical.

More specifically, this invention is concerned with an improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. it is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending with other products in making commercial antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyl-lead compounds where the likelihood of thermal decomposition is more of a problem.

As is well known, tetraalkyllead antiknock compounds generally are produced by reacting a sodium lead alloy with an alkyl halide. Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer a problem. However, the tetraalkyl-le-ad compound so produced is in admixture with various reaction by-products from which it must be separated. Separation is effected by steam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due to the toxic and unstable nature of tetra-alkyllead antiknock compounds, these distillation and purification operations are subject to many difficulties.

In these distillation and purification operations meticulous temperature control and exact safety measures are of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperature where thermal decomposition becomes appreciable. For example, decomposition of tetraethyllead occurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetraethyllead from the reaction products accompanying its synthesis. At temperatures above 100 C., the decomposition rate increases logarithmically so that a point is soon reached where external heat is no longer required and decomposition becomes self-propagating.

Such likelihood of excessive decomposition is present also during blending, handling, storage, and transportation. Prior to diluting the alkyllead concentrate with scavengers, gasoline or other materials, the alkyllead co pound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally well below that of decomposition. For example, in the purification step wherein the tetraethyllead concentrate is washed and blown with at atmospheric temperature to remove impurities, a sudden increase in temperature may occur due to the oxidation of triethylbismuth which is present as an impurity. Also pumps used in handling tetraethyllead occasionally freeze and the friction developed may cause 3,133,105 Patented May 12,1964

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a local overheating to a temperature above the temperature of decomposition of the tetraethyllead. Faulty wiring, leaks onto steam pipes, and other accidental causes also may produce local overheating with resulting dangerous decomposition.

It is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated state-viz. separation, purification, blending, transportation, and storage-the likelihood of excessive thermal decomposition must be provided for and effectively combatted.

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: separation, purification, blending, transportation and storage.

The above and other objects of this invention are accomplished by incorporating with alkyllead compounds a relatively small quantity of a material which has the property of inhibiting alkyllead thermal decomposition. The foregoing objects are 'also accomplished by conducting one or more of the foregoing operations in the presence of such a material.

The thermal stabilizer of this invention is turpentine.

Concentrations of this thermal stabilizer ranging from.

A feature of invention is the fact that turpentine is a readily available, inexpensive material having a high order of effectiveness when utilized as described above,

As known to those skilled in the art, various suppliers make available various grades of so-called wood turpentine all of which are very eifectively used pursuant to this invention. It follows therefore that the present invention accomplishes its objectives in a simple and economical manner.

An interesting feature of this invention is the fact that tilled turpentine can be used to advantage in conducting this invention. 7

Another unique feature of this invention is the experimental finding that turpentine is more effective, especially at the lower concentrations, than very closely related materials known heretofore as thermal stabilizers for alkyllead compounds. In particular, it has been found that common turpentine is more elfective than such materials as alpha-terpineol, cyclohexene, and dipentene, all of which are disclosed for use as thermal stabilizers U.S. 2,660,59 1-596 inclusive. Although alplia-pineney the chief constituent of wood turpentine is also very eifectively used in accordance with this invention the available experimental data indicates that the gross mixture of turpentine is even more effective than the talplia-pinene itself.

The chief thermal decomposition products of alkyllead compounds are lead metal and hydrocarbon gas. Hence, a very good index of alkylllead thermal decomposition is liberation of this gas.

To illustrate the effectiveness of this invention, a series of direct comparisons were made of the decomposition characteristics of unstabilized and stabilized tetracthyllead samples. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction tube. A 100 cc. gas buret beside the bath, and equipped with a water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steady temperature of 195 C., the sample-containing tube was quickly immersed in the bath and clamped with the levelling bottle adjusted to hold the gas buret in place at a zero reading. 'I hen measured was the time during which the sample was held at 195 C. without pronounced thermal decomposition and consequent evolution occurring. Thus, the longer the time, the more thermally stable was the alkyllead composition.

With. pure tetraethyllead used in 1 ml. amounts, pronounced thermal deterioration occurred almost immediately as evidenced by rapid gas evolution. In tact, the decomposition of unstabilized tetraethyllead will normally become uncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possible to very rapidly cool it down to about 100 C. or below.

The remainder of the compositions tested in the manner described above and the results thereby obtained are shown the following table.

TABLE Eflect of Additives on Thermal Decomposition of Alkyllead Compounds at 195 C.

It will be noted that the wood turpentine utilized in Run 1 pursuant to this invention exhibited a much higher degree of thermal stabilizer effectiveness than identical concentrations of the prior art materials used in Runes 2-4. A still further demonstration of the unusually great efiectiveness of turpentine is seen in the fact that when employcd in the above test procedure with tetnaethyllead at a concentration of weight percent based on the weight of tetraethyllead the induction time at 195 C. was 170 minutes.

The above-described beneficial behavior of the thermal stabilizer of this invention also takes place with other alkyllead compounds such as tiniethylle-ad bromide and tetnapropyllead. In fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapted to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess alkyl halide have been discharged trom the autoclave. For example, the termal stabilizer may be added in appropriate quantity to the alkyllead reaction concentrate just before the separation step 'Which is conducted at a 4 temperature close to the temperature Where hazardous runaway decomposition is particularly prevalent. By adding the above thermal stabilizer to the reaction concentrate just prior to distillation, the danger arising from unexpected temperature increases is substantially eliminated.

Most prebferably the above thermal stabilizer is employed to stabilize the alkyllead compound both in storage and in shipping and especially to stabilize any alkyllead concentrate, i.e., compositions containing at least percent by weight of alkyllead compound. If elevated temperature conditions are likely to be encountered, the addition of a small amount of themal stabilizer to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved. While meticulous temperature control and exacting safety measures have been successful in reducing to a minimum the hazards of processing and handling of tetraethyllead, the use of this invention provides a much greater factor of safety. Furthermore, waste of the alkyllead product due to decomposition is considerably minimized through the use of this invention.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satis fied by an alkyl radical. For example rtetraethyllead, tetra-methyllead, tetrap-ropyllead, dimethyldiethyllead, triethylplienyllead, and triethyllead bromide can be successfully stabilized against thermal decomposition by incorporating therein a relatively small quantity of one of the thermal stabilizers of this invention. This invention is particulamly well suited to the stabilization of any mixture involving two or more of the following compounds: tetramethyllead, ethyltrimethyllead, diethyldimethyllead, tniethylmethyllead, and tetraethyllead.

What is claimed is:

1. A method of inhibiting the decomposition of an alkyllead compound at temperatures of from about C. to about C. which comprises incorporating with said compound from about 0.5 to about 30 weight percent of turpentine based on the weight of the alkyllead compound.

2. In the process of producing an alkyllead compound by reacting a sodium lead alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation in the presence of from about 0.5 to about 30 weight percent of turpentine based on the weight of the .alkyllead compound.

3. A concentrated alkyllead compound with which has been blended from about 0.5 to about 30 weight percent of turpentine based on the weight of the alkyllead compound.

4. lhe composition of claim 3 wherein said compound is selected from the group consisting of tetramethyllead, ethyltrimethyllead, diethyldimethyllead, triethylmethyllead, tetnaethyllead, and mixtures thereof.

5. The composition of claim 3 wherein said compound is tetraethyllead.

References Cited in the file of this patent FOREIGN PATENTS 718,567 Great Britain Nov. 17, 1954 

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUND AT TEMPERATURES OF FROM ABOUT 100* C. TO ABOUT 195*C. WHICH COMPRISES INCORPORATING WITH SAID COMPOUND FROM ABOUT 0.5 TO ABOUT 30 WEIGHT PERCENT OF TURPENTINE BASED ON THE WEIGHT OF THE ALKYLLEAD COMPOUND. 